WebAssembly.Memory()

The WebAssembly.Memory() constructor creates a new Memory object which is a resizable ArrayBuffer that holds the raw bytes of memory accessed by a WebAssembly Instance.

A memory created by JavaScript or in WebAssembly code will be accessible and mutable from both JavaScript and WebAssembly.

Syntax

var myMemory = new WebAssembly.Memory(memoryDescriptor);

Parameters

memoryDescriptor

An object that can contain the following members:

initial

The initial size of the WebAssembly Memory, in units of WebAssembly pages.

maximum Optional

The maximum size the WebAssembly Memory is allowed to grow to, in units of WebAssembly pages. When present, the maximum parameter acts as a hint to the engine to reserve memory up front. However, the engine may ignore or clamp this reservation request. In general, most WebAssembly modules shouldn't need to set a maximum.

Note: A WebAssembly page has a constant size of 65,536 bytes, i.e., 64KiB.

Instance methods

Increases the size of the memory instance by a specified number of WebAssembly pages (each one is 64KB in size).

Examples

There are two ways to get a WebAssembly.Memory object. The first way is to construct it from JavaScript. The following example creates a new WebAssembly Memory instance with an initial size of 10 pages (640KiB), and a maximum size of 100 pages (6.4MiB).

var memory = new WebAssembly.Memory({initial:10, maximum:100});

The second way to get a WebAssembly.Memory object is to have it exported by a WebAssembly module. The following example (see memory.html on GitHub, and view it live also) fetches and instantiates the loaded memory.wasm byte code using the WebAssembly.instantiateStreaming() method, while importing the memory created in the line above. It then stores some values in that memory, then exports a function and uses it to sum some values.